Variable speed motor control circuit

Abstract

A control system and method for controlling the speed of a PSC motor having an auxiliary winding configured to provide torque for initial motor startup and a run winding configured to provide continuous motor operation. The motor is coupled to a capacitor configured to direct a portion of a current through the run winding when the PSC motor reaches its intended speed. The control system includes a speed control unit coupled between a voltage line and the PSC motor and a bypass circuit coupled between the voltage line and the capacitor via a first path. The speed control unit is configured to variably control the speed of the PSC motor. The bypass circuit is configured to receive a control signal from the speed control unit via a second path and to regulate a chopped voltage wave form generated by the speed control unit such that at least a portion of the chopped voltage wave form is not applied to the capacitor.

1. A control system for controlling the speed of a variable speed permanent split capacitor (PSC) motor having an auxiliary winding configured to provide torque for initial motor startup and a run winding configured to provide continuous motor operation, the motor being coupled to a capacitor configured to direct a portion of a current through the run winding when the PSC motor reaches its intended speed, the control system comprising:
 a speed control unit coupled between a voltage line and the PSC motor, wherein the speed control unit is configured to control the speed of the PSC motor; and 
 a bypass circuit coupled between the voltage line and the capacitor via a first path, wherein the bypass circuit is configured to receive a control signal from the speed control unit via a second path and to regulate a chopped voltage wave form generated by the speed control unit such that at least a portion of the chopped voltage wave form is not applied to the capacitor. 
 
   
   
     2. The control system of  claim 1 , wherein the bypass circuit is configured such that no portion of the chopped voltage wave form is applied to the capacitor. 
   
   
     3. The control system of  claim 1 , wherein the run winding is configured to receive the chopped voltage wave form. 
   
   
     4. The control system of  claim 1 , wherein the control signal comprises the chopped voltage wave form. 
   
   
     5. The control system of  claim 1 , wherein the bypass circuit is configured to regulate the chopped voltage wave form when the control signal is received. 
   
   
     6. The control system of  claim 1 , wherein the control signal is variable from a low level to a high level. 
   
   
     7. The control system of  claim 6 , wherein the control signal is inclusive of a pulse width modulated signal. 
   
   
     8. The control system of  claim 1 , wherein the speed control is configured to electronically disconnect the PSC motor from the voltage line to halt operation of the PSC motor, and the bypass circuit is configured to electronically disconnect the capacitor from the voltage line when the PSC motor is electronically disconnected from the voltage line. 
   
   
     9. The control system of  claim 8 , wherein the capacitor is electronically disconnected from the voltage line when the control signal to the bypass circuit drops to a low DC level. 
   
   
     10. The control system of  claim 8 , wherein the PSC motor and the capacitor are electronically disconnected from the voltage line irrespective of whether the voltage line is energized. 
   
   
     11. The control system of  claim 1 , wherein the regulation of the chopped voltage wave form by the bypass circuit is synchronized with the speed control unit. 
   
   
     12. The control system of  claim 1 , wherein the run winding and the auxiliary winding are independently and electronically controlled. 
   
   
     13. The control system of  claim 1 , wherein the bypass circuit comprises a pair of triacs and a pair of optoisolators, wherein the pair of optoisolators are operated by the control signal to turn on the pair of triacs such that the capacitor is coupled to the voltage line. 
   
   
     14. The control system of  claim 13 , wherein the pair of optoisolators are operated by the control signal to turn off the pair of triacs such that the capacitor is disconnected from the voltage line. 
   
   
     15. The control system of  claim 1 , wherein the bypass circuit comprises a triac and a pair of optoisolators, wherein the pair of optoisolators are operated by the control signal to turn on the triac such that the capacitor is coupled to the voltage line. 
   
   
     16. The control system of  claim 15 , wherein the pair of optoisolators are operated by the control signal to turn off the triac such that the capacitor is disconnected from the voltage line. 
   
   
     17. The control system of  claim 1 , wherein chopped voltage wave form comprises variable portions of a voltage wave form. 
   
   
     18. The control system of  claim 1 , wherein the voltage line is neutral. 
   
   
     19. A method for controlling the speed of a variable speed permanent split capacitor (PSC) motor having an auxiliary winding configured to provide torque for initial motor startup and a run winding configured to provide continuous motor operation, the motor being coupled to a capacitor configured to direct a portion of a current through the run winding when the PSC motor reaches its intended speed, the method comprising:
 coupling a voltage line and the PSC motor with a speed control unit configured to control the speed of the PSC motor; 
 coupling the voltage line and the capacitor with a bypass circuit via a first path; 
 receiving by the bypass circuit a control signal from the speed control unit via a second path; and 
 regulating by the bypass circuit a chopped voltage wave form generated by the speed control unit such that at least a portion of the chopped voltage wave form is not applied to the capacitor. 
 
   
   
     20. The method of  claim 19 , wherein the chopped voltage wave form is regulated such that no portion of the chopped voltage wave form is applied to the capacitor. 
   
   
     21. The method of  claim 19 , further comprising receiving by the run winding the chopped voltage wave form. 
   
   
     22. The method of  claim 19 , wherein regulating the chopped voltage wave form occurs when the control signal is received. 
   
   
     23. The method of  claim 19 , wherein the control signal is variable from a low level to a high level. 
   
   
     24. The method of  claim 23 , wherein the control signal is inclusive of a pulse width modulated signal. 
   
   
     25. The method of  claim 19 , further comprising:
 electronically disconnecting via the speed control the PSC motor from the voltage line to halt operation of the PSC motor; and 
 electronically disconnecting via the bypass circuit the capacitor from the voltage line when the PSC motor is electronically disconnected from the voltage line. 
 
   
   
     26. The method of  claim 19 , further comprising independently and electronically controlling the run winding and the auxiliary winding. 
   
   
     27. The method of  claim 19 , wherein the bypass circuit comprises at least one triac and a pair of optoisolators, wherein the method further comprises operating the pair of optoisolators to turn on the at least one triac such that the capacitor is coupled to the voltage line when the control signal is received. 
   
   
     28. The method of  claim 27 , further comprising operating the pair of optoisolators to turn off the at least one triac such that the capacitor is disconnected from the voltage line. 
   
   
     29. The method of  claim 19 , wherein coupling the voltage line and the PSC motor with a speed control unit comprises coupling the voltage line to the bottom of the run winding of the PSC motor via the speed control unit. 
   
   
     30. The method of  claim 29 , further comprising coupling a second voltage line to the top of the run winding of the PSC motor. 
   
   
     31. The method of  claim 30 , wherein the second voltage line is neutral.